1. Technical Field of the Invention
This invention relates generally to portable electronic equipment and more particularly to a multi-function handheld device.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radio, a pager, cellular telephones, computer memory extension (commonly referred to as a thumb drive), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer, data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
As is also known, many handheld devices include an input port that connects to a microphone such that audio inputs may be received and subsequently recorded (i.e., stored in a digital format). To facilitate the digital storing of audio input signals, at least one integrated circuit of the handheld device includes a microphone input pin that is coupled to receive the audio signals via the input port. The microphone input pin is biased via an on-chip microphone biasing circuit that establishes an AC ground for the analog input signals. The biased analog signals are then converted to digital signals, which may be stored in this format or converted to another format (e.g., pulse code modulation).
An issue with the on-chip microphone biasing circuit is that, since it typically includes a resistive divider network coupled to the power supply of the integrated circuit, it injects power supply noise into the biased analog signals. The injection of power supply noise, or any other noise, into the analog signals limits the signal quality as it is converted to digital signals. Further, such a resistive divider network microphone biasing circuit constantly consumes power, which for a battery operated handheld device, is detrimental.
Therefore, a need exists for a microphone bias circuit that reduces noise injected into analog input signals.